2011年10月3日星期一

Intersex is due to genes exchange between sex chromosomes or uneven division in Meiosis

1 Definition of intersex

Intersex, in humans and other animals, is the presence of intermediate or atypical combinations of physical features that usually distinguish female from male. It has 4 cases.

1.1Female pseudohermaphroditism

In this case the sex chromosomes are XX and the female has ovaries, but also external male sex organs (penis).

1.2Male pseudohermaphroditism

They have XY as sex chromosomes, but their external organs are not fully developed or they are completely female on the outside.

1.3 True hermaphroditism

While the above were “pseudohermaphroditism”, meaning they are mostly male or mostly female, in this case there are both testicles and ovaries.

1.4 Complex or Undetermined Intersex Disorders –Many chromosome configurations other than simple 46 XX or 46 XY can result in disorders of sex development. These include 45, XO (only one X chromosome), and 47, XXY, 47, XXX -- both cases have an extra sex chromosome, either an X or a Y. These disorders do not result in an intersex condition where there is discrepancy between internal and external genitalia.

As is known to all, Chromosomal crossing-over is an exchange of genetic material between homologous chromosomes. It is one of the final phases of genetic recombination, which occurs during prophase I of meiosis in a process called synapsis. Synapsis begins before the synaptonemal complex develops, and is not completed until near the end of prophaseI. Crossover usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome.

But experts thought that the crossing-over just occurs during Non-sister chromatids in 22 pairs of autosomes, but sex chromosomes often remain unpaired, because the X and Y chromosomes are very different from each other in their genetic composition. That is the key point of intersex. Physical exchange of homologous chromosomal regions by homologous recombination during prophase I is absolute, and Non-exchange is relative. It is easy to understand, as same as the movement is absolute, and static is relative. Intersex is the typical results of crossing-over between X and Y chromosomes. Precisely, intersex is just only one typical result of numerouspossibilities caused by crossing-over between X and Y chromosomes.I think there are wealth of contents in X and Y chromosomes, not only unitary control boy or girl. Here I am going explain them one by one case.

2.1 Case 1 Female pseudohermaphroditism

when the father’ sex chromosomes have crossing-over during meiosis I, the Y chromosome give some chromatid segments to X chromosome, and get some alleles back, which only control the offspring have a small clitorisora big penis, but not control other information. Then the father gives his exchanged Xf chromosome to his daughter then his daughter has XmXf chromosomes, but she indeed has male penis instead of female clitoris. Here, Xm means X chromosome with some male reproductive traits, and Xf means X chromosome with whole female reproductive traits. There is anotherkey factor that all thegenes that control sextrait aredominant inheritance. As a result, the daughter’ Xm chromosome from her mother can’t express out, and she only can express dominant traitfrom his father’s exchanged Xf chromosome. The result is the girl has a male penis.

2.2 Case 2 male pseudohermaphroditism

It is as same as case 1, but the father gives his exchanged Yf chromosome to his son. Although, his son has XfYf chromosomes, he indeed has female clitoris instead of male penis, because the genes whatever in Xf chromosome from his mother or exchanged Yf chromosome from his father are invisibleinheritance. The result is the boy don’t have male penis, though he has XfYf chromosomes. Here, Yf means Y chromosome with some female reproductive traits.

We can say that the above “pseudohermaphroditism” ‘culprits arethe fathers.More specifically, where did Father'sgenescome from? Of course from grandparents. In other words,Female pseudohermaphroditism- the grandfather’ part of sex genes inherited to granddaughter through his son, and granddaughter expressed male trait from her grandfather’ genes. Male pseudohermaphroditism- the grandmother’s part of sex genes inherited to grandson through her son, and grandson expressed female trait from his grandmother’ genes, not from his mother. I think this point is veryimportant for researching intersex.

The above two kinds of ambiguous genitalia isthe result ofallelicexchange between X chromosome and Y chromosome. The people in this situation whatever Female pseudohermaphroditism or Male pseudohermaphroditism have 46 chromosomes and can producegerm cells. Because the probability of crossing-over occurrence during sex chromosomes is very small, we can ignorethe crossing-over again. The following is their offspring genes tape after affected father with normal mother (Table 1) and normal father with affected mother (Table 2).

2.3 Case 3 true hermaphroditism

This extreme example of hermaphroditism is quite rare. I am not so sure, I guess it is also due to the crossing-over partial occurrence between X chromosome and Y chromosome, but not allelicexchange, it is non-allelic crossing-over between sex chromosomes. As the result, the people also have 46 chromosomes, but the sex chromosome must have structural abnormalities.A portion of the chromosome is duplicated, resulting in extra genetic material instead of a portion of the same chromosome is missing or deleted. The sex trait the people expressed is they have the 2 homologous organs.

2.4 In case 4 complex or Undetermined Intersex Disorders

This situation can’t be explained by crossing-over between sex chromosomes and I think it is related touneven division during Meiosis I or Meiosis II.In Anaphase Meiosis I, the centromere breaks, but sex homologous chromosomes not separate, and go to one of two haploid daughter cells together (Figure 1 and Figure 4). In Anaphase Meiosis II, the centromeres break, but sister chromatids not separate to haploid daughter cells (Figure 2 and Figure 5). Figure 3 and Figure 6 are both uneven division in Meiosis I and Meiosis II.

Figure 1 The type of gametes with father’s Meiosis I uneven division but Meiosis II even division

Figure 2 The type of gametes with father’s Meiosis I even division but Meiosis II uneven division

Figure 3 The type of gametes with father’s Meiosis I and II both uneven division

Figure 4 The type of gametes with mother’s Meiosis I uneven division but Meiosis II even division

Figure 5 The type of gametes with mother’s Meiosis I even division but Meiosis II uneven division

Figure 6 The type of gametes with mother’s Meiosis I and II both uneven division

Due to very small proportion of abnormal gametes, there is very low probability to meet between two abnormal gametes. So we can ignore this situation, and just research on the case which is one is normal the other is abnormal. Table 3 shows us the offspring’s gene tape with abnormal father’s gamete mated normal mother’s gamete, and table 4 is the offspring’s gene tape with normal father’s gamete mated abnormal mother’s gamete. It is noteworthy that the all gene types with red color have been found already, not only this, so far people didn’t find any another sex-chromosome Anomaly not in my table 2 and table 3. I think that is very strong evidence to my theory. About why does YO not existence? I think the reason must be related to the gene with YY not exist neither.

3 Conclusions

I think sex chromosomes not only determine sex, they also have genes for many functions we don’t know yet. There is no absolutemaleand female. Physical exchange of homologous chromosomal is absolute, and Non-exchange is relative. Intersex person is just one of us. Notice here: the gene type with black normal in Table 3 and 4. It means maybe you are the reproduction of uneven division both in Meiosis I Meiosis II, if you are with so-called normal genes. Maybe lesbian, gay and bisexual are all because of crossing-over during sex chromosomes.